Construction of Ships

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ship construction, naval architecture, hull, keel, steel, frames, bulkheads, bow, anchor, tank, stern, propeller, shafting, rudder, captain, engineer, officer, bridge, cargo hold, hatches, engine room, Marine, Engineer, Shipping, Marine, Engineer, Engineering, Shipping, Ship, Equipment, Machinery, Merchant, Shipping
 

Hull
The hull is the main body of the ship that floats on the water. In order to provide the maximum space to store cargo, the hull is constructed with a rectangular cross section. The fore and aft centerline of the ship is called the keel. The keel is the skeleton of the ship's hull. It is made strong enough to withstand the many different forces on the ship's hull. Other portions like the corner edges (bilge keels, sheerstrake) are also strengthened. 

In order to float, the steel ship must have a large volume compared to the weight. The steel plates (about 10 mm thick) will not be able to resist the buoyancy forces on their own. Frames are used to support the steel plates. Some ships are framed horizontally, while others are framed transversely. At high loading areas the frames are enlarged. These are called web frames.

The lower portions of the hull are made stronger as compared to the higher portions. This is to cater for the higher loads (pressure) on the hull deeper underwater. 

The bottom of the hull is made into tanks for fuel oil, fresh water, and ballast seawater. These are called double bottom tanks. This type of construction reduces the chance of flooding of the ship in case of any damage to the outer hull plates. 

In case of heavy damage which puncture even the tank top plates, the ship is prevented from sinking by bulkheads. Bulkheads are continuous walls that divide the ship into many sections. The purpose of these bulkheads is to isolate the flooded sections from the rest of the ship.

Bow
The front of the ship is called the bow. To give it less resistance to forward motion, the bow is made into a wedge shape. Some ship bows have a spherical shape at the submerged portion. These are called bulbous bows. The bulbous bow is constructed to give better efficiency to the ship by streamlining the wave flow.

The bow of the ship is strengthened against slamming from the waves. The inside the bow contains the anchor chain and the forepeak tank. The trim of the ship can be adjusted by ballasting seawater at the forepeak tank (and aft-peak tank located at the stern). 

Stern
The back portion of the ship is called the stern. Although the submerged portion is made into a streamline shape, the visible top section can be rounded or flat. The stern contains the propeller, propeller shaft, stern tube, and the rudder.

The propeller acts like a screw when it turns in the water. The propeller is rotated at low speeds of 100 to 150 rpm, so that the water can flow smoothly through the blades. By avoiding air bubbles forming in the water, cavitation erosion on the propeller is reduced. 

The main engine through the shafting inside the engine room rotates the propeller. The propeller shaft is the shaft that is fitted with the propeller at one end and coupled to the main engine shafting at the other. The propeller shaft rotates inside the oil lubricated stern tube, fitted with bearings. Seawater is prevented from entering the tube by the stern tube seals. Older ships have shaft gland packing and lignum vitae bearings that are lubricated by the seawater. 

The rudder is a hinged plate (foil shaped) which can be turned through a certain number of degrees either to starboard or to port. The turning of the rudder plate is done through the rudderstock. The rudderstock is supported at the steering gear room on bearings. More information on the steering gear can be obtained from Steering Gear


  Accommodation
This portion of the ship is usually painted a different color from the hull. Portholes are visible whenever there is a cabin. The accommodation of the crew can also be part of the hull. The bridge is the highest level on the ship. This is the central lookout point on the ship. The accommodation of the Captain, Chief Engineer, and Radio Officer are usually just below the bridge. Further down are the accommodations for the other officers, dining saloon, officer lounge, and others.

All the cabins surround the center engine room space that is in the middle. The funnel is where the exhaust gas from the main engine, boiler, and auxiliary engines emerges. The funnel bears the distinguishing mark of the shipping line. 

The lifeboats are usually located one level above the main deck. For cargo ships, there are usually 2 lifeboats, one on the portside and another on the starboard. In addition, there will be life rafts on this deck and some on the bridge deck.
Engine Room
The engine room houses all the machinery necessary for the propulsion of the ship. The area stretches from the lowest tank top of the hull to the highest funnel area. If the shafting connecting the main engine to the propeller is long, there will be a shaft tunnel joining the engine room to the stern tube. In such a case, the shafting will have to pass through the bulkhead of another compartment. A remotely operated watertight door is installed to separate the two compartments in case of flooding in one of these.

The engine room has at least two escape routes. In case of fire, flooding or any other disaster, the engine room personnel can escape through any one of them. 

The engine room doors, skylight, ventilation ducts can be sealed tight if there is a need to control a major fire in the engine room.

In the areas near the accommodation, sound insulation materials are installed to dampen the noise from the machinery.

Cargo Hold
Cargo holds are spaces for carrying dry cargo. Each cargo hold is covered by a hatch cover, which can be opened for cargo handling, and closed when the ship is underway. Most cargo hatch covers can be folded up when opened to save space. Container ships may have one-piece cargo hatches because the shore cranes are always available for their handling.

Tankers have tanks instead of cargo holds. As the liquid cargo is pumped in and out, there is no cargo hatches but only manhole covers and vent openings. The deck above the tanker is covered with pipes and valves.

 

2004 Yoon Chee Tuck    Contact me

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